Signaling system



1945' R. L. H OLLlNGSW( JRTH I 2,382,567

SIGNALING- SYSTEM 2 Sheets$heet 1 Filed June '7, 1943 ATTORNEY Aug. 14,-1945.

R. L. HOLLINGSWORTH SIGNALING SYSTEM Filed June 7, 1943 2 Sheets-Sheet 2kmmmmgmd INVENTOR f [5: AQZ4WJWPM ATTOR N E Y Patented Aug. 14, 1945SIGNALING SYSTEM R3? Lee Hollingsworth, Riverhead, N..Y.,.assi'gnortoRadio Corporation of America,.a'c0rporation of Delaware ApplicationJune 7:, 1943, Serial No. 489,915

21 Claims. (01. 250-17) I This application discloses anew methodfof andmeanszfor' improving amplitude modulated radio wave transmission.

- My: new method and'rneans is particularly applicable to transmissionof amplitude modulated wave energy within the secondary service area.

In the system of my invention I control the intensity or amplitudeofacarrier wave being modulated in accordance with signals to therebymaintain the desired degree or percentage of modul'ati'on totherebyreduce distortion.

In modulatedradio wave transmission, using amplitude-modulation, suchasis in general use mane standard broadcast frequency bands and in I theinternational short wavefrequency bands it isthe' praotice in many casesto make extensive use of'the-s'econdary coverage area. This'area isreachedbyway of reflection from the Heaviside layer-in the'upperatmosphere. The continual shifting-of-this reflection mediumproducesmultiple-wave fronts, that inturn produces fading within. thereceiving antenna, since these various reflected electro magneti'c wavefronts arrive at the antenna' out of phase. ln-amplitudemodulationreception, if distor- -'ti'on is to be avoided, there must be asuflloi'ency carrier'or a substantial portion thereof is lost intransmission, distortion equivalent to over-modulation will occurcontinually over the secondary coverage area where fading is continuallytaking place, especially during high percentage modulation intervals. f

. It is an object of thisinvention, thereforato improve the.transmission of amplitudemodulatedl electro -magnetic' waves-"in thesecondary service area. I

. It is an additional object of this invention to improve thetransmission of long distance shortwave modulated radio wave energy.

The manner inwhich the above objects and other objects are attained willappear from the detailed description of my invention which fol lows. Inthiscdescription referencewill be made to the two figures-in thedrawings P Thexdescription of my invention follows and reference.isimade to Fig. rot theaccompanying drawings; component parts of thisinventi'onfare identified as. follows and their principle functionisexplained. Numeral l. represents the radio frequency energy input from aconstant frequency-generator at the assigned carrier frequency. Thisenergy passes through a tuned transformer consisting, of tuned primarywinding 2 andtuned secondary: winding 3, to excite radio frequencyamplifier 4. The output of radio frequency amplifier tube 4 is coupledto radio frequency amplifier-tube 9 via tuned coupled circu-i ts 1 and 8for further amplification The output. of'tube 9'i -r1- turn excitesradio frequency am plifier tubelava tuned coupled circuits [2 and M. 10, I 5; and 1 are bias resistors, while 6, H, and [B are radio"frequency bypass condensers. Theplatesuppl y connections are indicatedby numeral l3. From tube l6 the carrier wave energy isfed-to the antennaM via tuned coupled circu-i-ts i9 and. Ground potentialthroughout thisdrawing is indicated by 22. 'Thus; a radiated carrier source ofelectro'magnetic wave energy is-indic'ated. i

Coupled to the" unmodulated radio frequency carrier source is tunedcoupling coil 23 which connects to radio frequency amplifier 24,theoutput of' which connects vi-alead s 25-, tuned coupled-- circuits 26and Zl'to the plate oftriode tube 28-; "it'hisrariio" frequency energyserves as a'substitute for a battery supply to cause triode tube to beconductive to produce a negative bias voltage across resistance 29whi'ch 'isthe plate load "resistance for tube 28; Lead 30 supplies thisbias'to the control grids of radio frequency amplifier tubes4,9-a-nd--l6. This'bia-s represents the fixed bias supplyfor theseamplifier tubes together withtheir-bias supplies from resistances l0;ligand l'l', until high' percentage'modulation isapplied to thesuppressor grid of tube l6;

The modulation from a microphone or another usable source is applied atterminals '31, and passes through limiter 32 where the amplitude levelis automatically controlled when'it reaches a value corresponding tomodulation in the transmitter tube l6. This is a practice generally usedthroughout the broadcastingindustry. The output oflim-i-ter tube 32 ispassed 'through audio frequency transformer 33 toamplifier tube 34 3%?is a bias resistorfor'tube 34; Transformer 36 couples the amplifiedoutput of tube-34 via lead 3ft to'the suppressorgrid' of tube I 6tomodu'latethe carrier frequencysupplied." thereto. Thistype ofmodulation is usedfor simplicity of illustration, however, it is'withinthe scope of this invention 'that other types of amplitude}modulation'cou'ld'be used. 1 I r a diode tube which passes current inone direction only from across resistance 4| into time delay circuit 4|and 42. The ratios of transformer secondary windings of transformer 33are such that rectifier 39 does not become conductive until themodulation level reaches approximately 40% of full modulation.

The operation of my invention is as follows: Let us assume that carrierwave energy is being radiated. Modulation at 40% is applied and the biasamplifiers 4, 9 and I6 remain unchanged. Now let us assume that themodulation level is raised to 50%. Rectifiertube 39 draws current andbuilds up a negative drop across resistance 4| which is applied to thegrid of triode 28 through diode '43 via time delay circuit 4|. and 42,reducing the current through triode 2.8; decreasing the bias on radiofrequency amplifiers 4, 9, and I6, thus increasing the carrier energy toestablish again a condition comparable to modulation at a level of 40%.As the modulation goes higher in level above 40% the higher goes thecarrier level to insure in so far as possible a sufliciency of carrierwave energy, over the secondary coverage area of an amplitude modulatedwave transmitter.

The variation of broadcast modulations takes place suddenly, thus therapid action through diode 43 to the control-grid of triode 28 increasesthe carrier level instantaneously with sudden rises in modulation. Timedelay values4l and 42 cause a slight holdover to provide smoothness ofoperation between wide variations in modulation level. I

It is within the scope of this invention that the action of this circuitbe applied only to a radio frequency amplifier supplying modulatedcarrier wave energy to a radiator, the 'characteristicsof which wouldhave only a high angle of radiation to improve secondary area coverage,while the modulated carrier energy is simultaneously fed to a radiatorin a conventional manner which has a characteristic suitable only forprimary or ground wave coverage, Explaining further, assume that WEAF orany other clear channel station use a one-half wave radiator for groundwave coverage in the primary service area, and that the radiation goesout over this radiator modulated up to 100%. Assume another radiatorhaving an electrical length of from .62 to 1.0 wavelength, depending onthe radiation angle desired to render secondary service. This radiatoris then fed with the same radio frequency carrier source, through anamplifierstage which is operated in the manner described inthisspecification to supply a strong carrier supply throughout thesecondary service area and to always maintain the equivalent of from 40to 60 per cent modulation, insuring improvement of reception throughoutthe secondary service area, in that distortion due to fading would begreatly reduced. It is possible to select the proper angle of radiationto cause improved reception in the critical area,-located in the regionswhere the groundwaveis fast diminishing in field strength, and where thesky wave is increasing in intensity.

Such an arrangement is shown in Fig. 2, wherein 50 is the carriersource, 56 is the controlled amplifier such as, for example, as shown inFig. 1, 2| is the high angle radiator for secondary area coverage, 60 isthe amplitude modulator operating from say 0 to 100% modulation, and 64is the 2 radiator for primary service area coverage.

Further, it may be desirable to focus 'WEAF or any other clear channelstation to cover all of Mexico and Central America at night, or to reachdown Rio Way and at the same time render their normal domestic clearchannel service in the United States. Such could be done very well withpotentials which includes these steps, amplifying said carrier waveenergy, controlling said amplification of said carrier wave energy inaccordance with the amplitude of said original carrier wave energy,modulating the amplitudeof the carrier wave energy in accordance withthe modulating potentials and increasing the amplification of thecarrier wave energy when the amplitude of the modulating potentialsexceeds a selected'value.

2. A method of signaling by means of wave energy of carrier wavefrequency and of substantiallyconstant amplitude and modulatingpotenmodulating potentials. which exceeds a selected magnitude a controlpotential and increasing theamplification of the carrier wave energy inaccordance with the derived control potential.

3. A method ofsignaling by means of wave energy of carrier wavefrequencyand of substantially-constant amplitude and modulating potentials whichincludes these steps, amplifying said carrier wave energy,rectifying'carrierwave energy and controlling said amplification-of saidcarrier wave energy in accordance with resulting rectified components,modulating the amplitude of the amplifiedcarrier wave energy inaccordance with the modulating potentialsrectifying modulatingpotentials which exceed a selected magnitude and increasing-theamplification of the carrier wave energy in accordance with therectified modulating potentials. '1

4. In a'signaling system of the class described, a source of wave energyof carrier wave frequency and of substantially constant amplitude, atsource of modulating, potentials; an amplifier having an inputcoupled tosaid sourceof wave energy and having an output, "means excited .bysaidjwave energy for deriving a biasing potential depending on theamplitude .of said carrier. and applying said biasing potential to saidamplifier, means for modulating saidcarrier wave energy in accordancewith said modulating potentials; andrmeans for-- supplementing saidfirst: mentioned biasing potential to increase: the-gain of saidamplifier and the amplitudev of the carrier when themodulatingpotentials. exceed a. selected magnitude.

5. In a signaling. system of the class described, asource of wave:energy of carrier wave frequency and of substantially constantamplitude, a source exceed. a selected value: for supplementing. saidfirst mentioned. biasing potential to increase the acticn-of-saidvamplifier and the amplitude of the carrier fed to the modulator.

6., Ina signalingsystem of the. class described, resource of wave'energyof carrier wave frequency and. of:v substantially constant amplitude, asource ofmodulatingpotentials, an amplifier having an input coupled tosaid'source of wave energy and having an output, a modulator coupled tothe output. of said amplifier, a rectifier coupled. to

said, an'iplifier and excited by said wave energy for deriving a biasingpotential for controlling thegain-of. said amplifier to supply carrierwave energyto said. modulator of selected amplitude,

connections excited by potentials from said modulatin-g potentialsourcefor applying modulating potentials to said modulator anda secondrectifier associated with said. amplifier and excited by modulatingpotentials from saidmodulating potential source whichexceed a'selectedvalue for applying. to said amplifier biasing. potentials in addition tosaid first mentioned biasing potential toincrease the action of saidamplifier and the amplitude of the carrier fed to the modulator.

7-..In a system ofautomatic carrier compensation in modulated carrierwavetransmission-including a carrier wave source of electric-magneticwave energy, a carrier-wave radio frequency amplifier, means formodulating said carrier wave radio frequency energy in accordance withapplied electric. waveenergy a sourceof negative selfbias for said radiofrequency amplifier, the value of which varies with changes in theamplitude of the carrier wave and a separate negative bias supply forsaid radio frequency amplifier that is automatically variable inverselyto the level of the applied modulation level when said modulation levelreaches a predetermined value.

8. In a system of automatic carrier compensation in modulated carrierwave transmission including a carrier Wave source of electro-magneticwave energy, a means of carrier wave radio frequency amplification, ameans for modulating said carrier wave radio frequency ener y,aradiating means, a source of negative self-bias for each individualradio frequency amplifying tube, the value of which varies with changesin the amplitude of the carrier wave and a separate negative bias supplyfor said radio frequency amplifiers that is automatically variableinversely'to the level of the applied modulation level when saidmodulation level reaches a predetermined value.

9. In a system of automatic carrier compensation in modulated carrierwave transmission including'a carrier'wave-seurce 0t electroemagneticwas/e: energy, :acarrier wave: radio frequency am? plifler including aplurality of amplifier tubes coupled incascade, a modulation source andmeans. for "modulating said. radio frequency carrier energy, a.separatenegative bias supply for at. least one of said radio frequencyamplifying tubes; saidsepara-te negative. bias. supply comprisingazrectifieriexcited by .theunmodulatedcarrier wave energy; and a. secondrectifier excited. .by the. modulating voltage; when said modulationleve1: exceeds av predetermined value and a coupling between said.rectifiers'for controlling said firstrectifierbycurrent rectifiedbysaidsecond rectifier.

10. A system of automatic carrier compensation inmoclulated: carrierwave transmission; including a.- carrier wave; source of. electro-magnetic wave eneIg-y,..a means of: carrier wave-radio frequencyamplificationncomposed of amplifier 1 tubes operating in. cascade, aradiating means, a source of negative self-bias for at least. oneof saidradio amplify-ing'tubes, asource and. means of modulatingisaid radiofrequency carrier'energy, a separate negative biassupply forat least oneof. said radio; frequency amplifying. tubes, said; separate negativebias supply comprising an amplifierexcited by the .iuunodulated carrierwave energy, and. aarectifier coupled tosaid amplifier said rec:-tifier-consisting; of. a -triode tube which is. grid controlled, a;second. rectifier which is responsive to the, modulating; voltage when.said modulation level exceeds apredetermined value, and'a oneway diodetube and a time delay circuitcoupling said second rectifier to the gridof the triode reculation level exceedsv apredetermined" level value,

anda sky wave-radiator connected to said second means. V

, 12.,A source of carrier wave energy, a first means .for amplifying andmodulating, saidcarrier wave energy from zero to 100% andzconnect led.to a. ground wave radiator, a; second meansfor separately amplifyingsaid carrier wave energy and modulating same, said second carrier Waveamplifying means being capable of expanding the power output thereofwhen the applied modulation level exceeds a predetermined level value,and a sky wave radiator coupled to said second amplifying means.

13. A method of signaling by means of wave energy of carrier wavefrequency and 0f substantially constant amplitude and modulatingpotentials which includes these steps, amplifying said carrier waveenergy, rectifying carrier wave energy and controlling saidamplification of said carrier wave energy in accordance with resultingrectified components, modulating the amplitude of the amplified carrierwave energy in accordance with the modulating potentials, rectifyingmodulating potentials which exceed a selected magnitude and controllingthe rectification of the carrier wave energy in accordance with therectified modulating potentials.

14. In a signaling system, a source of wave energy of carrier wavefrequency, an electron discharge amplifier stage having input electrodescoupled to said source and having output electrodes from which amplifiedmodulated carrier wave energy may be derived, a controllable tuberectifier in a circuit including an impedance, a coupling between theimpedance andzthe input electrodes of said amplifier, connections forimpressing wave energy of carrier wave frequency on said rectifier, asource of modulating potentials coupled to said amplifier for modulatingthe carrier wave energy, and a second rectifier coupled to said sourceof modulating potentials electrodes of said amplifier, a coupling tosaid rectifier for impressing wave energy of carrier Wave frequency onsaid rectifier, a source .of modulating potentials coupled to saidamplifier stage for modulating the carrier wave energy, and a secondrectifier coupled to said source of modulating potentials and connectedto the control grid of said first rectifier for controlling the actionthereof. V

17. In a signaling system, a source of wave energy of carrier wavefrequency, an electron discharge amplifier stage having input electrodesincluding a control grid coupled to 'said source and having outputelectrodes from which amplified modulated carrier wave energy may bederived, a tube rectifier having a control grid and having outputelectrodes connected through an output impedance, connections forimpressing wave energy of carrier Wave frequency on said rectifier, acoupling between the control grid of the amplifier and said'impedance tosupply the drop in potential across said impedance as a bias to the gridof said amplifier, a source of modulating potentials coupled to saidamplifier for modulating the carrier wave energy, a second rectifiercoupled to said source of modulating potentials and connected to a loadimpedance, and a connection between said last named impedance and thecontrol grid of said first rectifier for controlling the action thereofin accordance with rectified modulating potentials.

s 18. A system as recited in claim 17, wherein time elementsare includedin said last named connections.

19. In a signaling system, a carrier wave amplifier'tubehaving inputelectrodes including a grid and cathode excited by carrier wave energyand output electrodes from which amplified modulated carrier wave energymay be derived; a first rectifier tube of the control grid type havingan anode and cathode connected by an impedance, a connection between theend of said impedance adjacent the cathode of said. rectifier and thegrid of said amplifier tube, a connection between the other end of saidimpedance and the cathode of said amplifier tube, connectionsforimpressing wave energy ofcarrier wave frequency on said rectifier, asource of modulating potentials coupled by a modulation circuit to saidamplifier tube, a second rectifier having an anode and having a cathodeconnected to the cathode of said first rectifier, a second impedanceconnecting the anode of the second rectifier to the cathode of thesecond rectifier, a connection between the anode end of the secondimpedance and the grid of the first rectifier, and means for impressingmodulating potentials on said second rectifier.

20. A system as recited in claim 19, including a time delay network inthe last connection.

21. In a signaling system, a carrier wave amplifier having inputelectrodes excited by carrier wave energy and output electrodes fromwhich amplified modulated carrier wave energy may be derived, a firstrectifier tube of the control grid type having as a load an impedanceconnected with the input electrodes of said amplifier for biasing thesame, connections for impressing wave energy of carrier wave frequencyon said first rectifier, a source of modulating potentials coupled by amodulation circuit to saidamplifier, a second rectifier inseries with animpedance associated with the grid of said first rectifier, and meansfor impressing'modulating potentials on said second rectifier.

R. LEE HOLLINGSWORTH.

